Method and apparatus for implementing adaptive reordering of data recovery procedure steps in a disk drive

ABSTRACT

A method and apparatus are provided for implementing adaptive reordering of data recovery procedure (DRP) steps in a direct access storage device (DASD). An initial set of DRP steps is stored. A reorder table is stored during the operation of the DASD. The reorder table includes data recovery data for each data head of successful predefined DRP step numbers. When a DRP process is started, checking for a modified DRP step is performed using the reorder table. Responsive to not identifying the modified DRP step, file parameters for a DRP read operation are set based on the initial set of DRP steps. Responsive to identifying the modified DRP step, file parameters for a DRP read operation are set based on a reordered DRP step that is identified by using the stored successful predefined DRP step numbers in the reorder table. When a successful DRP read operation is identified, the data recovery data in the reorder table are updated. The reordered DRP step is an identified most frequently occurring DRP step number in the reorder table for the current data head. The data recovery data for each data head stored in the reorder table includes a number of total errors, a number of errors above a set threshold, and a reorder flag. The reorder flag is set based upon the number of errors above the set threshold being at least a predefined percentage of the number of total errors. When the reorder flag is set, a reordered DRP step is identified using the stored successful predefined DRP step numbers in the reorder table.

FIELD OF THE INVENTION

The present invention relates generally to the data processing field,and more particularly, relates to a method and apparatus forimplementing adaptive reordering of data recovery procedure steps in adirect access storage device (DASD).

DESCRIPTION OF THE RELATED ART

Computers often include auxiliary memory storage units having media onwhich data can be written and from which data can be read for later use.DASDs or disk drive units incorporating stacked, commonly rotated rigidmagnetic disks are used for storage of data in magnetic form on the disksurfaces. Data is recorded in concentric, radially spaced datainformation tracks arrayed on the surfaces of the disks. Transducerheads driven in a path toward and away from the disk axis of rotationwrite data to the disks and read data from the disks. Data located on aparticular track on a disk surface is read or written by properlypositioning a data transducer head directly over the track. In order tomaintain the head in proper position over the data track, servo systemstypically are incorporated into disk drives.

When problems arise detecting the customer data in a DASD, a datarecovery procedure is started. All DASDs have operations or datarecovery procedure (DRP) steps including multiple read operations thatare performed in an attempt to correctly detect the customer data. FIG.2 illustrates a conventional data recovery procedure for a disk drive.When an unsuccessful read operation is identified at decision block 204,then the DRP process is started. Predetermined file parameters are setbased on the DRP step information at block 208 and the DRP step isperformed. When an unsuccessful read operation for the DRP step isidentified at decision block 210, then the DRP step is incremented to anext step in the DRP table. Then the predetermined file parameters areset based on this DRP step information at block 208 and the next DRPstep is performed. As shown in FIG. 2, in known DASDs or disk drives,predefined data recovery procedure (DRP) steps are executed in a fixedorder. For example, the first step is typically to read the same data onthe next disk revolution, the 11th step might be to try to reset themagnetic head state by performing a dummy write. There may be, forexample, 50 to 100 DRP steps used by a DASD or more DRP steps may beused depending on the architecture. The DRP steps are always the sameand the process to retrieve the data follows the set of DRP steps in afixed order.

A need exists for a mechanism to more efficiently implement datarecovery procedures in a direct access storage device (DASD).

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a method andapparatus for implementing adaptive reordering of data recoveryprocedure steps in a direct access storage device (DASD). Otherimportant objects of the present invention are to provide such methodand apparatus for implementing adaptive reordering of data recoveryprocedure steps substantially without negative effect and that overcomemany of the disadvantages of prior art arrangements.

In brief, a method and apparatus are provided for implementing adaptivereordering of data recovery procedure (DRP) steps in a direct accessstorage device (DASD). An initial set of DRP steps is stored. A reordertable is stored during the operation of the DASD. The reorder tableincludes data recovery data for each data head of successful predefinedDRP step numbers. When a DRP process is started, checking for a modifiedDRP step is performed using the reorder table. Responsive to notidentifying the modified DRP step, file parameters for a DRP readoperation are set based on the initial set of DRP steps. Responsive toidentifying the modified DRP step, file parameters for a DRP readoperation are set based on a reordered DRP step that is identified byusing the stored successful predefined DRP step numbers in the reordertable. When a successful DRP read operation is identified, the datarecovery data in the reorder table are updated.

In accordance with features of the invention, the reordered DRP step isan identified most frequently occurring DRP step number in the reordertable for the current data head. The data recovery data for each datahead stored in the reorder table includes a number of total errors, anumber of errors above a set threshold, and a reorder flag. The reorderflag is set based upon the number of errors above the set thresholdbeing at least a predefined percentage of the number of total errors.When the reorder flag is set, a reordered DRP step is identified usingthe stored successful predefined DRP step numbers in the reorder table.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIG. 1 is a schematic and block diagram representation illustrating adirect access storage device (DASD) for implementing methods foradaptive reordering of data recovery procedure steps for a disk drive inaccordance with the preferred embodiment;

FIG. 2 is a flow chart illustrating a conventional data recoveryprocedure for a disk drive;

FIG. 3 is a diagram illustrating an exemplary reorder table forimplementing adaptive reordering of data recovery procedure steps for adisk drive in accordance with the preferred embodiment;

FIG. 4 is a flow chart illustrating exemplary sequential steps forimplementing adaptive reordering of data recovery procedure steps for adisk drive in accordance with the preferred embodiment; and

FIG. 5 is a block diagram illustrating a computer program product inaccordance with the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Having reference now to the drawings, in FIG. 1 there is illustrated adirect access data storage device (DASD) or disk drive generallydesignated as 100 for implementing adaptive reordering of data recoveryprocedure (DRP) steps for the disk drive 100 in accordance with thepreferred embodiment. As shown in FIG. 1, disk drive 100 includes astack 104 of disks 106 each having at least one magnetic surface 108.The disks 106 are mounted parallel to one another for simultaneousrotation on and by an integrated spindle and motor assembly 110.Information on each magnetic disk surface 108 is read from or written tothe disk surface 108 by a corresponding transducer head assembly 112movable in a path having a radial component across the rotating disksurface 108.

An arm 114 carries each transducer head assembly 112. The arms 114 areganged together for simultaneous pivotal movement by a voice coil motor(VCM) magnet assembly or actuator 116. Drive signals applied to the VCMmagnet assembly 116 cause the arms 114 to move in unison to position thetransducer head assemblies 112 in registration with information storagetracks on the disk surfaces 108 where information is written or read.

Disk drive 100 includes a read/write channel 120 coupled to thetransducer head assemblies 112 and coupled to a disk drive controller122 that generates signals controlling the operation of variouscomponents of the disk drive 100. Disk drive 100 includes a disk driveinterface 124 coupled to the disk drive controller 122 and a memory 126.A host computer (not shown) provides data read and write commands to thedisk drive, and data signals are transmitted to or from the transducerhead assemblies 112.

Disk drive controller 122 is suitably programmed for implementingadaptive reordering of data recovery procedure steps for the disk drive100 in accordance with the preferred embodiment. Disk drive controller122 is suitably programmed to generate a reorder table of the preferredembodiment as illustrated in FIG. 3 and to execute the flow functions ofthe preferred embodiment as illustrated in FIG. 4.

In accordance with features of the preferred embodiment, the disk drive100 adaptively reorders the DRP steps so that the DRP step or DRP stepsmost likely to succeed are executed first. The reordered DRP step orreordered DRP steps are identified using most frequently occurringsuccessful DRP steps that are stored with recovery procedure data in areorder table of the preferred embodiment. For some situations, theconventional DRP order wastes time. For example, if it is known thatresetting the head state works 90% of the time for a particular head112, then it is wasteful to perform all of the steps leading up to thishead state resetting step. It is better to try resetting the head first.For example, resetting the head multiple times are performed beforetrying off-track reads and the like which might typically precede thedummy write step. While the example of head instability has been given,there are other situations where reordering the DRP is advantageous.Therefore, a further aspect of the invention is to execute DRP steps ina logical manner depending on the nature of the recovery. For example,if for a given head and data zone data is normally recovered usingeither a 10 or 20% off-track position toward the disk ID, then whenexecuting a DRP for this head, the DRP steps using ID off-trackpositions are used first for data recovery.

The invention begins by having a disk drive microprocessor or controller122 create a reorder table 300 that shows, for each head, a number M of5 last DRP step numbers that resulted in a successful recovery of data.Assuming a drive with 4 heads, a result might look like thoseillustrated in the following simplified example of Table 1. In Table 1,the last 5 DRP steps for heads 0 through 3 that resulted in successfuldata recovery are given. The example Table 1 shows that head 2 usuallyrecovers on DRP step 11, while heads 0 and 1 recover on steps 1 or 2.Head 3 recovers on either steps 8 or 10 which can be assumed to be inthe same off-track direction.

TABLE 1 Head DRP(1) DRP(2) DRP(3) DRP(4) DRP(5) Mode 0 1 2 1 2 1 1 1 1 11 1 1 1 2 11 11 11 11 13 11 3 8 10 10 8 10 10

The second step that the invention performs is to calculate thestatistical mode of the DRP step numbers for each head. The mode isdefined as the most frequently occurring DRP step number in a storedsequence. The last column in Table 1 gives the mode for the last 5 DRPsteps. Based on the modes for each head, heads 0 and 1 can continue touse the normal DRP ordering, that is step 1, step 2, step 3, and thelike. For head 2, however, a better DRP order of reordered DRP steps isstep 11, step 13, step 3, and the like.

The DRP steps can be reordered for this simple example shown in theabove Table 1 in the following way:

Head 0: Step 1, Step 2, Step 3, . . . .

Head 1: Step 1, Step 2, Step 3, . . . .

Head 2: Step 11, Step 13, Step 3, . . . .

Head 3: Step 10, Step 8, Step 3, . . . .

The DRP also can be ordered to include single retries or reread stepsfirst in case early recovery does occur as follows:

Head 0: Step 1, Step 2, Step 3, . . . .

Head 1: Step 1, Step 2, Step 3, . . . .

Head 2: Step 1, Step 2, Step 11, Step 13, Step 5, . . . .

Head 3: Step 1, Step 2, Step 10, Step 8, Step 5, . . . .

In accordance with features of the preferred embodiment, the disk drive100 adaptively reorders the DRP steps for a given head, zone, and thelike, at a predefined periodic interval, such as once every hour, or theadaptation can take place during periods of high DRP use. The inventioncan also be selectively applied to drives that are suffering dataperformance degradation.

Referring now to FIG. 3, there is shown an exemplary reorder tablegenerally designated as 300 for implementing adaptive reordering of datarecovery procedure steps for disk drive 100 in accordance with thepreferred embodiment. As shown in FIG. 3, reorder table 300 stores eachhead (and zone) 302, a plurality of DRP buckets (1)—DRP (N) 304, a mode306, a total errors 308, a number of errors above a threshold 310, and areorder flag 312. Reorder table 300 is simplified for understanding theinvention, with zone information not separately included in reordertable 300. Each of the plurality of DRP buckets (1)—DRP (N) 304 storethe successful DRP steps identified during disk drive operations whenprocessing each sequential data recovery procedure following a failedread operation of the disk drive 100. The total errors 308 are updatedfor each error processed including the initial DRP steps and the numberof errors above a threshold 310 are updated for each error processedover a set threshold. The stored values in the total errors 308 togetherwith the number of errors above a threshold 310 are used to determinewhen the DRP step for a particular head 302 should be reordered and thenthe reorder flag 312 is set. The mode 306 stores the most frequentlyoccurring DRP step stored in the DRP buckets (1)—DRP (5) 304.

At power up of disk drive 100, the reorder table 300 can be empty or allfields 304, 306, 308 and 310 initially can be zero. Disk drive 100stores a set of initial normal DRP steps that are, for example, asfollows:

1. Reread; 2. Reread; 3. Reread; 4. Reread; 5. Reread; 6. Reread; 7.Off-track reread +5%; 8. Off-track reread −5%; 9. Off-track reread +10%;10. Off-track reread −10%; 11. Start reread operation 2 bytes earlier;12. Start reread operation 2 bytes earlier; 13. Off-track reread +15%;14. Off-track reread −15%; 15. Off-track reread +18%.

In accordance with features of the preferred embodiment, a user selectedthreshold of a predefined number of steps, such as 6 initial DRP stepsare performed before any values are put into the DRP buckets (1)-DRP (5)304 sections of the reorder table 300. This is due to the fact thatinitial DRP steps 1 through 6 are simple rereads and it is not untillater steps that file parameters are changed in the disk file 100.However, the total errors 308 are updated for each error processedincluding the initial DRP steps. The stored values in the total errors308 together with the number of errors above a threshold 310 are used todetermine when the DRP step for a particular head 302 should bereordered and then the reorder flag 312 is set. For example, when thenumber of errors above a threshold 310 are at least a predefinedpercentage of the total errors, such as, 30% and a value has been storedin all the DRP buckets (1)-DRP (5) 304, then the reorder flag 312 isset. The mode 302 stores the most frequently occurring or DRP stepstored in the DRP buckets (1)-DRP (5) 306 to be used for reordering DRPsteps when the reorder flag is set. It should be understood that themode 306 field can be used for storing multiple DRP steps, such as themost frequent or DRP step together with one or more next most frequentor next DRP steps.

Creating the reorder table 300 may be understood by considering thefollowing example 1 of read errors in disk drive 100:

Error # Error on Head DRP Step used 1 1 2 2 2 4 3 2 6 4 1 3 5 2 8 6 2 107 3 7 8 2 3 9 2 8 10 3 9 11 2 8 12 2 10 13 1 7 14 0 2 15 2 3

As can be seen, head 2 has had at least 5 errors over step 6 and this isover 50% of the total errors for that head, with 5 errors abovethreshold and 9 total errors. With this example 1, using the criteria ofreordering to be set when the errors above threshold 310 are greaterthan 30% of the total errors 308, the reorder flag is set for head 2 andresults in the reorder table 300 for Example 1 as follows:

REORDER TABLE 300 with errors above threshold 310 are greater than 30%of the total errors 308 for Example 1 Total Errors Head DRP(1) DRP(2)DRP(3) DRP(4) DRP(5) Mode Errors Above Reorder 302 304 304 304 304 304306 308 Threshold 310 Flag 312 0 0 0 0 0 0 0 1 0 0 1 7 0 0 0 0 0 3 1 0 28 10 8 8 10 8 9 5 1 3 7 9 0 0 0 0 2 2 0

In this case, the successful DRP step that is used the most is DRP step8 for head 2 followed by DRP step 10. Thus, when future errors are nowfound, reordering is used for head 2. For example, a predefined DRP stepafter a selected number of initial reread DRP steps, such as, DRP step 5will now be reordered to the mode DRP step 8 (Off-track reread −5%) andstep 6 will be reordered to the next mode DRP step 10 (Off-track reread−10%). The other steps can remain the same for now. Also, sincereordering has now occurred for head 2, any time step 5 is used it willbe listed as DRP step 8 from the reorder table 300, and step 6 will belisted as DRP step 10 from the reorder table 300. Also, the thresholdfor incrementing to the number of errors above threshold is now set forerrors above 4 DRP steps instead of 6 initial DRP steps for head 2 sinceonly 4 initial DRP reread steps are performed before the reordered steps5 and 6.

Considering the following example 2 of read errors in disk drive 100 asthe file continues to read:

EXAMPLE 2

Error # Error on Head DRP Step used 1 1 2 2 2 10 3 2 10 4 1 1 5 2 10 6 01 7 2 14

The oldest data is removed from the reorder table 300 first and the datarecovery data in the reorder table are updated with first in/first outmemory usage. With this example 2 and using the criteria of reorderingto be set when the errors above threshold 310 are greater than 30% ofthe total errors 308, results in the reorder table 300 as follows:

REORDER TABLE 300 with criteria of errors above threshold 310 aregreater than 30% of the total errors 308 for Example 2 Total No. ofErrors Head DRP(1) DRP(2) DRP(3) DRP(4) DRP(5) Mode Errors Above Reorder302 304 304 304 304 304 306 308 Threshold 310 Flag 312 0 0 0 0 0 0 0 2 00 1 7 0 0 0 0 0 5 1 0 2 10 10 10 10 14 10 13 9 1 3 7 9 0 0 0 0 2 2 0

Now, step 5 will be replaced with DRP step 10 (Off-track reread −5%) andstep 6 will be replaced with DRP step 14 (Off-track reread −15%). Thisprocess of generating the reorder table 300 continues until one of anumber of factors changes it, for example, such as, when the userdefined that a power cycle will reset the reorder table 300 or when theerrors for head 2 start to all be below the 30% threshold, so that steps5 and 6 become the initial DRP reread steps again.

FIG. 4 illustrates exemplary sequential steps for implementing adaptivereordering of data recovery procedure steps for a disk drive inaccordance with the preferred embodiment. When a command is given toread data from the disk, the file is set to read a data sector asindicated in a block 402. Checking whether the read operation wassuccessful is performed as indicated in a decision block 404. When theread operation was successful, then the sequential operations returnfrom the read operation and continue with other file operations asindicated in a block 406. Otherwise, when the read operation was notsuccessful or the read failed, then the DRP process is started bychecking whether to use a modified DRP step based on data in the storedreorder table 300 as indicated in a decision block 408. For example, thereorder flag 312 for the current data head is checked at decision block408. If a modified DRP step is not indicated, then the file parametersare set for a read operation based on normal DRP step information asindicated in a block 410. When the use of a modified DRP step isindicated based on the stored data in the stored reorder table 300, thenthe file parameters are set for a read operation based on reordered DRPstep information in the stored reorder table 300 as indicated in a block412. Checking whether the read operation was successful is performed asindicated in a decision block 414. When the read operation wassuccessful, then the recovery information is updated in the reordertable 300 including for the current data head and zone 302, thesuccessful DRP step number if above threshold in DRP bucket 304, mode306, total error and errors above a threshold numbers 308 and 310, andthe reorder flag 312 as indicated in a block 416. Then the sequentialoperations return from the read operation and continue with other fileoperations as indicated in a block 406. Otherwise, when the readoperation was not successful or the read failed, then the DRP processcontinues by checking whether all DRP reads have been completed asindicated in a decision block 418. When all DRP reads have beencompleted, then the read failed for all DRP steps and the sequentialoperations return from the read operation and continue with other fileoperations as indicated in a block 406. When all DRP reads have not beencompleted, then the DRP step is incremented to the next step in the DRPtable as indicated in a block 420. Then the sequential steps arecontinued returning to decision block 408 to again check whether to usea modified DRP step based on data in the stored reorder table 300.

Referring now to FIG. 5, an article of manufacture or a computer programproduct 500 of the invention is illustrated. The computer programproduct 500 includes a recording medium 502, such as, a floppy disk, ahigh capacity read only memory in the form of an optically read compactdisk or CD-ROM, a tape, a transmission type media such as a digital oranalog communications link, or a similar computer program product.Recording medium 502 stores program means 504, 506, 508, 510 on themedium 502 for carrying out the methods for implementing adaptivereordering of data recovery procedures of the preferred embodiment inthe disk drive 100 of FIG. 1.

A sequence of program instructions or a logical assembly of one or moreinterrelated modules defined by the recorded program means 504, 506,508, 510, direct the disk drive controller 122 for implementing adaptivereordering of data recovery procedures of the preferred embodiment.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

What is claimed is:
 1. A method for implementing adaptive reordering ofdata recovery procedure (DRP) steps in a direct access storage device(DASD) comprising the steps of: storing an initial set of DRP steps;storing a reorder table during operation of the DASD; said reorder tableincluding data recovery data for each data head including successfulpredefined DRP step numbers; starting a DRP process, checking for amodified DRP step using said reorder table; responsive to notidentifying said modified DRP step, setting file parameters for a DRPread operation based on a DRP step from said initial set of DRP steps;responsive to identifying said modified DRP step, setting fileparameters for a DRP read operation based on a reordered DRP step; saidreordered DRP step identified using said stored successful predefinedDRP step numbers in said reorder table; and identifying a successful DRPread operation and updating said data recovery data in said reordertable.
 2. A method for implementing adaptive reordering of data recoveryprocedure (DRP) steps as recited in claim 1 wherein the step of storingsaid reorder table including said data recovery data includes the stepsfor each data head of storing a number of total errors, a number oferrors above a set threshold, and a reorder flag.
 3. A method forimplementing adaptive reordering of data recovery procedure (DRP) stepsas recited in claim 2 wherein includes the steps for storing saidreorder flag includes the steps of setting said reorder flag based uponsaid number of errors above said set threshold being at least apredefined percentage of said number of total errors.
 4. A method forimplementing adaptive reordering of data recovery procedure (DRP) stepsas recited in claim 1 further includes the step for each data head ofstoring a mode; said stored mode identifying a most frequently occurringone of said stored successful predefined DRP step numbers.
 5. A methodfor implementing adaptive reordering of data recovery procedure (DRP)steps as recited in claim 1 wherein the step of setting file parametersfor a DRP read operation based on a reordered DRP step includes the stepof identifying a most frequently occurring one of said stored successfulpredefined DRP step numbers in said reorder table.
 6. A method forimplementing adaptive reordering of data recovery procedure (DRP) stepsas recited in claim 1 includes the steps of performing a predefinednumber of initial steps from said initial set of DRP steps before thestep of setting file parameters for a DRP read operation based on areordered DRP step.
 7. A method for implementing adaptive reordering ofdata recovery procedure (DRP) steps as recited in claim 1 wherein thesteps of identifying said successful DRP read operation and updatingsaid data recovery data in said reorder table includes the steps ofremoving oldest stored recovery data from said reorder table and storingsaid updated data recovery data.
 8. A method for implementing adaptivereordering of data recovery procedure (DRP) steps as recited in claim 7wherein the step of storing said updated data recovery data includes thestep of storing said successful DRP step number; updating a total errorsnumber; and updating a number of errors above a set threshold.
 9. Amethod for implementing adaptive reordering of data recovery procedure(DRP) steps as recited in claim 8 includes the step of setting a reorderflag responsive to said updated number of errors above said setthreshold being at least a predefined percentage of said number of totalerrors.
 10. A method for implementing adaptive reordering of datarecovery procedure (DRP) steps as recited in claim 1 includes the stepsof identifying a failed DRP read operation and incrementing to a nextstep in said stored initial set of DRP steps; and checking for saidmodified DRP step using said reorder table.
 11. Apparatus forimplementing adaptive reordering of data recovery procedure (DRP) stepsin a direct access storage device (DASD) comprising: a disk drivecontroller; a memory coupled to said disk drive controller for storingan initial set of DRP steps and a reorder table; said reorder tableincluding data recovery data for each data head; said disk drivecontroller for starting a DRP process, and checking for a modified DRPstep using said reorder table; said disk drive controller responsive tonot identifying said modified DRP step, for setting file parameters fora DRP read operation based on a DRP step from said initial set of DRPsteps; said disk drive controller responsive to identifying saidmodified DRP step, for setting file parameters for a DRP read operationbased on a reordered DRP step; said reordered DRP step being identifiedby using said said reorder table; and said disk drive controller foridentifying a successful DRP read operation and for updating said datarecovery data in said reorder table.
 12. Apparatus for implementingadaptive reordering of data recovery procedure (DRP) steps in a directaccess storage device (DASD) as recited in claim 11 wherein said diskdrive controller for identifying said successful DRP read operation andfor updating said data recovery data in said reorder table includes saiddisk drive controller for storing said successful DRP step number;updating a total errors number; and updating a number of errors above aset threshold.
 13. Apparatus for implementing adaptive reordering ofdata recovery procedure (DRP) steps in a direct access storage device(DASD) as recited in claim 12 includes said disk drive controller forstoring a reorder flag, responsive to said updated total errors number;and said updated number of errors above said set threshold. 14.Apparatus for implementing adaptive reordering of data recoveryprocedure (DRP) steps in a direct access storage device (DASD) asrecited in claim 13 includes said disk drive controller for setting saidreorder flag responsive to said updated number of errors above said setthreshold being at least a predefined percentage of said number of totalerrors.
 15. A computer program product for implementing adaptivereordering of data recovery procedure (DRP) steps in a disk drive, saidcomputer program product including a plurality of computer executableinstructions stored on a computer readable medium, wherein saidinstructions, when executed by a disk drive controller in the diskdrive, cause the disk drive controller to perform the steps of: storinga reorder table during operation of the DASD; said reorder tableincluding data recovery data for each data head; starting a DRP process,checking for a modified DRP step using said reorder table; responsive tonot identifying said modified DRP step, setting file parameters for aDRP read operation based on a DRP step from said initial set of DRPsteps; responsive to identifying said modified DRP step, setting fileparameters for a DRP read operation based on a reordered DRP step; saidreordered DRP step identified using said reorder table; and identifyinga successful DRP read operation and updating said data recovery data insaid reorder table.
 16. A computer program product for implementingadaptive reordering of data recovery procedure (DRP) steps as recited inclaim 15 wherein said instructions, when executed by a disk drivecontroller in the disk drive, for updating said data recovery data insaid reorder table includes the steps of: storing said successful DRPstep number; updating a total errors number; updating a number of errorsabove a set threshold; and setting a reorder flag responsive to saidupdated number of errors above said set threshold being at least apredefined percentage of said number of total errors.